I am trying to generate a model for applications where a polymer (such as ETFE, FEP, PTFE) is subject to different strains. Most empirical fatigue models are based on stress amplitude (empirical fatigue model not perfect I know - using tests data to validate).
However in applications where the strains are not fully reversed, is it ok to use a basic Smith-Watson-Topper model (as you would for metals) to correct for the mean stress effect or is there something more suitable for polymers? Or is it not necessary for polymers?
Thanks in advance.